The abbrevations you cite are not obscure.
As CD implies, "MDCM" is simply a fancier way of saying "MD": which as we all know is a four-year undergraduate programme offered by all medical schools.
The CCFP designation is available to general practitioners who have passed the College of Family Physicians of Canada's examination, and satisfied certain residency or equivalent practical experience requirements. Although it's not a particularly impressive medical qualification, someone who has it is certainly more qualified than a mere MD.
A Diploma in Aviation Medicine is rather more impressive. KCL's course is a specialist programme involving a six month residency, and its students generally must have past experience in aviation medicine. A somewhat less rigorous (part-time) D.Av.Med. programme is offered by
Otago University, New Zealand. Neither of the diploma programmes should be confused with the basic certificate programmes intended to provide only entry-level training for new aviation medical examiners: see e.g.
Otago (two semesters of part-time study, plus a two-day residential course), and
Monash, Australia (10 day residential course).